1. Field of the Invention
The present invention relates to clock recovery circuits, and more specifically to a method and apparatus for recovering data in serial communication channels
2. Related Art
Data tokens (e.g., a bit representing one of two possible values) are often transmitted from one system (“sender system”) to another (“receiver system”) using serial communication channels. In general, each data token is encoded in a corresponding analog signal portion, and the analog signal portions are transmitted in successive time intervals forming the serial communication channel. The sequence of data tokens are then recovered at a receiving end by sampling the analog signal portions at appropriate time points.
In a typical recovery approach implemented in a receiver system, a sampling clock is generated which specifies the specific appropriate time points for sampling a signal received on a serial communication channel. An ideal sampling clock generally causes the signal portions to be sampled in the center of (or within) a “data eye” portion in which the signal level closely represents an encoded data token.
One problem often encountered in data recovery is loss of data tokens, i.e., a data token encoded in an analog signal portion may not be recovered. The loss is often due to the inaccuracies in the generation of a sampling clock used to sample the signal received on a serial communication channel. The inaccuracies in turn are caused by factors such as jitter (short term disturbances), as is well known in the relevant arts.
Data loss generally leads to undesirable results, typically specific to the environment in which the data tokens are used. For example, in networking environments, a receiver system may request retransmission of a large data unit (e.g., packet) containing the unrecovered data, leading to unneeded retransmission overhead and potential slow-down of the end applications using the transmitted data. As another example, in display environments, loss of data representing a portion of an image frame may lead to poor image quality.
Therefore, what is needed is a method and apparatus to accurately recover data in serial communication channels.